High quality color inkjet printers, typically using cyan, magenta, yellow, and black inks (CMYK inks), strive to reproduce as best as possible the red, green, blue (RGB) image generated by a computer and displayed on a color monitor. Hence, the computer signals corresponding to the RGB tone values are converted to signals for ejecting cyan, yellow, magenta, and black ink droplets by the inkjet printer to reproduce the RGB image on the color monitor.
Techniques already exist for conversion of the RGB signals into corresponding CMYK signals for printing by the inkjet printer; however, these conversion techniques assume a nominal ink drop volume per nozzle by each of the print cartridges used in the inkjet printer. One particular print cartridge ejects an ink drop having a nominal volume of 8 picoliters from a nozzle when an energization signal is applied to an ink ejection element associated with the nozzle. Further detail regarding the operation of an inkjet printer may be found in U.S. Pat. No. 5,638,101 by Brian Keefe et al., entitled High Density Nozzle Array For Inkjet Printhead, incorporated herein by reference.
Due to fabrication variances, the ink drop volume for a print cartridge may differ by as much as 30% from the nominal value. This causes the calculated CMYK tone values to not accurately be represented by the final printed image on the medium. A lower ink drop volume for a cyan print cartridge, for example, causes a lighter cyan tone to be printed, and a higher ink drop volume causes a darker cyan tone to be printed. This problem is exacerbated when one color print cartridge in the printer (e.g., magenta) has a positive ink drop volume variance from nominal, while another print cartridge (e.g., yellow) has a negative ink drop volume variance. This not only distorts the brightness of the printed image but distorts the color (hue) printed as well.
Accordingly, what is needed is a technique for accurately reproducing color images using an inkjet printer which is independent of the ink drop volume variances of the color print cartridges used in the printer.